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Fat has a food energy content of 38 kilojoules per gram (9 kilocalories per gram) proteins and carbohydrates 17 kJ/g (4 kcal/g). [2] Water makes up a large proportion of the total mass ingested as part of a normal diet but it does not provide any nutritional value.
For example, fat (triglyceride lipids) contains 9 kilocalories per gram (kcal/g), while carbohydrates (sugar and starch) and protein contain approximately 4 kcal/g. [29] Alcohol in food contains 7 kcal/g. [30] The "large" unit is also used to express recommended nutritional intake or consumption, as in "calories per day".
Carbohydrates, on the other hand, are more highly hydrated. For example, 1 g of glycogen binds approximately 2 g of water, which translates to 1.33 kcal/g (4 kcal/3 g). This means that fatty acids can hold more than six times the amount of energy per unit of stored mass.
Structures of some common lipids. At the top are cholesterol [1] and oleic acid. [2]: 328 The middle structure is a triglyceride composed of oleoyl, stearoyl, and palmitoyl chains attached to a glycerol backbone.
It is involved in the process by limiting fat storage through inhibition of glucose intake and interfering with other adipose metabolic pathways. [1] The inhibition of lipogenesis occurs through the down regulation of fatty acid and triglyceride gene expression. [ 10 ]
In animals, these fats are obtained from food and are synthesized by the liver. [1] Lipogenesis is the process of synthesizing these fats. [2] [3] The majority of lipids found in the human body from ingesting food are triglycerides and cholesterol. [4] Other types of lipids found in the body are fatty acids and membrane lipids.
For example, the values for glucose, sucrose, and starch are 15.57, 16.48 and 17.48 kilojoules per gram (3.72, 3.94 and 4.18 kcal/g) respectively. The differing energy density of foods (fat, alcohols, carbohydrates and proteins) lies mainly in their varying proportions of carbon, hydrogen, and oxygen atoms.
In humans and many animals, fats serve both as energy sources and as stores for energy in excess of what the body needs immediately. Each gram of fat when burned or metabolized releases about nine food calories (37 kJ = 8.8 kcal). [5] Fats are also sources of essential fatty acids, an important dietary requirement.